Polyether polyols are often manufactured commercially using a catalyzed reaction of initiators having active hydrogen atoms with epoxides such as, for example, ethylene oxide and/or propylene oxide. Alkalinity is introduced into the polyether polyols, for example, by using alkaline metal hydroxides as catalysts.
Potassium hydroxide (KOH) and sodium hydroxide (NaOH) are some examples of typical alkaline catalysts used. In general, the metal hydroxide catalyst is added to the starter (usually a hydroxyl group containing compound), and equilibrium between the metal hydroxide and the starter occurs. This equilibrium is as shown in the following equation (using KOH as the alkaline catalyst):KOH+ROH⇄H2O+RO−K+
Both the hydroxide and the alkoxide can react with epoxides. This is often acceptable for short chain (low molecular weight) polyols, but the reaction of water is undesirable in the preparation of higher molecular weight (i.e., number average molecular weight of at least 1000) ethylene oxide capped polyols. It is therefore, necessary to force the above equilibrium to the right by removing the water (i.e., dewatering). This converts all of the hydroxide to alkoxide. The total amount of alkalinity remains constant and is equal to the amount of KOH originally added.
Once the polymerization of the epoxide(s) is completed, the alkaline catalyst is typically neutralized and removed from the crude mixture to yield the final polyether polyol. Several processes for the removal of the residual catalysts from the crude polyether polyols to yield the final product are known.
For example, in some cases, the polyether polyol undergoes a batch distillation after being neutralized. This distillation can occur at various temperatures and pressures. Moreover, during the distillation, some polyols, such as long chain active polyols, form a foam layer on top of the liquid product that rises up, and, if it rises high enough, it can overflow into the vessel's vent line, which can result in wastewater contamination and/or the need for manual cleaning of downstream equipment. As a result, in some cases, it may be necessary to decrease product batch sizes in order to minimize the occurrence of such “foam over”, which hinders productivity.
As a result, it would be desirable to provide a process for removing water from a polyether polyol in a vessel by batch distillation that can significantly reduce the frequency of foam-over and, in some cases, may even allow for the batch sizes to be increased in order to utilize more of the reactor capacity.
The present invention was made in view of the foregoing.